i dropped the plan to run slack on that pi. reasons being:
1. the rpi 3b+ isn't supported by the project. i'm worried to be left alone with important fixed. it works
2. i couldn't find a bare installer for the non-current release 15 for the pi. there are no directories for it. i know it could be done nevertheless, takes more effort
3. release 15 is compiled for armv7. i guess that also means it's 32-bit only
4. i don't want to hammer the sd with daily updates from current
5. the pi will be directly facing the wrath of the big bad internet. hence i can't compromise on security (because of current) and stability (also because of it)